1. Field of the Invention
The present invention relates generally to the fabrication of multichip modules having reduced dimensions and overall complexity. More specifically, modules capable of carrying multiple integrated circuit devices (hereinafter ICs or chips) are formed on a flexible carrier such that functional subsystems, i.e. complex areas of computer functions, such as memory, processors, graphics, SCSI adapters, I/O drivers, and the like can be placed on the flexible carrier.
2. Description of Related Art
It is currently known to attach many different
configurations of chips to flexible carriers. For example U.S. Pat. No. 4,967,950 shows the attachment of a controlled collapse chip connection (C4) type of IC directly to a flexible substrate. Other configurations of chips can also be attached to flexible substrate material, including pin through hole (PTH) packages, wire bonding and surface mount technology (SMT) chips wherein leads are aligned on solder pads and the solder is then reflowed.
Further, conventional technology has the capability of packaging multiple chips in various package configurations on a flexible substrate to form complex areas, or islands that can be used to provide specific functions. U.S. Pat. No. 4,567,543 shows a double sided flexible module that can receive a plurality of SMT and PTH packages. U.S. Pat. No. 4,495,546 describes a flexible substrate with a plurality of chips thereon that can be inserted into a connection slit on a motherboard. U.S. Pat. No. 5,028,983 discloses a film having beam leads with one end extending outward from the film to contact a substrate, and the other end to be bonded to the contact pads of an IC. C4 type chips are shown attached to a flexible carrier by use of an interposer type arrangement in U.S. Pat. No. 4,987,100 and 4,937,707. IBM TDB "Concept for Forming Multilayer Structures for Electronic Packaging" describes placing chips onto a flexible film which is then folded back on itself with a heat spreader device disposed between the sides of the film.
It is also known to use the complex areas, created when plural interconnected chips are attached to flexible substrate, to provide various functions in different types of electronic devices. For example. U.S. Pat. No. 4,177,519 and 4,081,898 describe using a flexible carrier with electronic components thereon to manufacture calculators. Further, the manufacture of wrist watches using functional areas is shown by U.S. Pat. No. 4,598,337 and 4,064,552. A camera lens including a flexible printed circuit board with chips thereon is described by U.S. Pat. No. 4,990,948. U.S. Pat. No. 4,843,520 shows an electronic circuit module with electronic components attached to a flexible film that is attached to first and second substrates. U.S. Pat. No. 4,104,728 describes an electronic apparatus with a flexible substrate, having a wiring pattern formed thereon which is disposed in a housing.
It can be seen that flexible carriers with integrated circuit devices attached thereon to form flexible circuits is well known in the art. However, current demands on the computer industry require that more functionality be placed in a smaller area, which can be packaged more efficiently by a computer system designer. In order to provide more functionality. multichip modules (MCM) have been utilized wherein the modules are attached directly to a planar board, or a circuit card. This method has several drawbacks including the high cost of the carrier to which the MCM is attached (due to the complexity of the MCM I/Os) and problems with efficiently interconnecting the module input/outputs (I/Os). Another problem, shown in the related art is the area required to attach and interconnect chips which are mounted on flexible carrier. That is. "fan-out" is required whereby leads extend from the chip to the periphery of the MCM or flex substrate for interconnection between the chips and other electronic devices, or other levels of packaging.
Therefore, it can be seen that a means of efficiently providing a functional subsystem consisting of plural densely placed electronic devices for use in a computer would be very desirable.